Guidance for External PSK Usage in TLS
draft-ietf-tls-external-psk-guidance-02

Document Type Active Internet-Draft (tls WG)
Authors Russ Housley  , Jonathan Hoyland  , Mohit Sethi  , Christopher Wood 
Last updated 2021-02-24 (latest revision 2021-02-20)
Replaces draft-dt-tls-external-psk-guidance
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Intended RFC status Informational
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Document shepherd Sean Turner
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tls                                                           R. Housley
Internet-Draft                                            Vigil Security
Intended status: Informational                                J. Hoyland
Expires: 24 August 2021                                  Cloudflare Ltd.
                                                                M. Sethi
                                                                Ericsson
                                                               C.A. Wood
                                                              Cloudflare
                                                        20 February 2021

                 Guidance for External PSK Usage in TLS
                draft-ietf-tls-external-psk-guidance-02

Abstract

   This document provides usage guidance for external Pre-Shared Keys
   (PSKs) in Transport Layer Security (TLS) version 1.3 as defined in
   RFC 8446.  It lists TLS security properties provided by PSKs under
   certain assumptions and demonstrates how violations of these
   assumptions lead to attacks.  It discusses PSK use cases,
   provisioning processes, and TLS stack implementation support in the
   context of these assumptions.  It provides advice for applications in
   various use cases to help meet these assumptions.  It also lists the
   privacy and security properties that are not provided by TLS when
   external PSKs are used.

Discussion Venues

   This note is to be removed before publishing as an RFC.

   Source for this draft and an issue tracker can be found at
   https://github.com/tlswg/external-psk-design-team.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

Housley, et al.          Expires 24 August 2021                 [Page 1]
Internet-Draft   Guidance for External PSK Usage in TLS    February 2021

   This Internet-Draft will expire on 24 August 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  Notation  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  PSK Security Properties . . . . . . . . . . . . . . . . . . .   3
     4.1.  Shared PSKs . . . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  PSK Entropy . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   5
   6.  External PSK Use Cases and Provisioning Processes . . . . . .   6
     6.1.  Provisioning Examples . . . . . . . . . . . . . . . . . .   7
     6.2.  Provisioning Constraints  . . . . . . . . . . . . . . . .   8
   7.  Recommendations for External PSK Usage  . . . . . . . . . . .   8
     7.1.  Stack Interfaces  . . . . . . . . . . . . . . . . . . . .   9
       7.1.1.  PSK Identity Encoding and Comparison  . . . . . . . .  10
       7.1.2.  PSK Identity Collisions . . . . . . . . . . . . . . .  10
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     10.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   This document provides guidance on the use of external Pre-Shared
   Keys (PSKs) in Transport Layer Security (TLS) version 1.3 [RFC8446].
   This document lists TLS security properties provided by PSKs under
   certain assumptions and demonstrates how violations of these
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